@Strange67 Welcome to the forum I advise you to write a only message with all your doubts, it will be easier to help you and to collect the information.
The meter glass serves to estimate, fix that I say, the number of carbon hydrrates, therefore it is used with patient who use insulin feathers and with patients with insulin pump. It helps you know how many hydrates you eat, but insulin needs change with each person, lifestyle, conditions, hormones, etc.That is why I tell you that it is an estimate.
There are many applications for the calculation of carbohydrates, tables, etc ... I used at the beginning the tables of the Diabetes Foundation, they went well, at 3 months you do not use them because you learn for yourself.I used the scale to measure everything ... It doesn't really need.In two weeks, by eye, you are able to calculate.
In diabetes we measure carbohydrates, but everything we eat requires insulin;Fats and protein also have to be taken into account, they are transformed into carbohydrates at approximately 4 hours.
In diabetes everything is proof and error.Do not be afraid to make mistakes, you eat normal and calculate a dose of insulin, if you are high at 2 hours, the next day you already know what you will need more insulin for those foods or a good walk or visit to the gym to eliminate them. You can also get more insulin at 2-3 hours, but a very small amount to correct.